Apparatus for testing pharmaceutical tablets



ZJMLWQ y F. D. SMITH ET AL APPARATUS FOR TESTING PHARMACEUTICAL TABLETS Fil'ed Feb. 19, 1954 J m w w H m A N A I n w w? {UM 1 I m 0 a WM I 5 tour.

Patented May 26, 1936 UNITED STATES PATENT oFricE APPARATUS FOR TESTING PHARMACEU- TICAL TABLETS tion of Delaware Application February 19, 1934, Serial No. 711,844

4 Claims.

This invention relates to the manufacture of pharmaceutical tablets, particularly those made by the compression of a granular product to pro- 1(:i uce a tablet of disc-like geometric configura- The object of the present invention is to provide a device for testing tablets by which the physical quality thereof may be judged and their suitability for packaging and sale ascertained.

Pharmaceutical tablets such, for example, as aspirin tablets have been made for many years. The tablets are manufactured by compressing a granulated mixture of aspirin and a binder, such as starch, within a form having the desired con- Notwithstanding the fact that the mechanical operations are standardized, the variability of the physical characteristics of the tab lets and their suitability for packaging and sale has never been controlled satisfactorily. One of the principal difiiculties incident to the study of these variables has been the fact that no satisfactory method or means for testing the product has been known. Heretofore the tablet manuiacturer has judged the physical quality of his product simply by its appearance and the facility with which one can break the tablet diametrically between his fingers. To this end the thumb of the hand is used as a fulcrum, which engages one face of the tablet, and the index and second fingers are used to apply a lever force from the opposite face of the tablet. This method of testing has been unsatisfactory for many reasons. Thus, no accurate estimate of the suitability of the tablet is obtained. Secondly, the results are not duplicative by other operators since no mathematical expression of the breaking point of the tablet can be had.

We have found that the crushing strength applied diametrically of the tablet is a suitable criterion of the desired physical qualities of a tablet and that the results obtained may be checked by difierent operators provided the crushing force is applied gradually against diametrically opposed points on the periphery of the tablet.

A better understanding of the device which we have invented for this purpose, may be had by referring to the accompanying drawing.

Figure l is the plane view of one embodiment of our invention which may be preferred;

Figure 2 is a sectional view taken along the line 2-2 in Figure 1; and,

Figure 3 is a sectional view taken along the line 3-3 of Figure l.

The device consists of a tubular member In which is externally threaded at both ends and includes a longitudinal slot ll. A tablet retaining member l2, consisting of a stirrup-like or U- shaped element of a somewhat trapezoidal contour which is open upon opposite sides to admit of disposing the tablets in peripheral contact with the loop and which is formed integrally with an internal threaded ring, is screwed to one end of the tube iii. A plunger element l3 adapted to engage the tablet is slidably mounted within the tube and is relatively movable with respect to the U-shaped tablet retaining member.

An internally threaded cap i5 is screwed to the opposite end of the tube and is itself provided with a coaxial threaded hole. Within the hole a mating, manually operable screw it is fitted, the end of which engages a shouldered guide element H which is slidably mounted in the tube. The guide fits loosely over the end of the screw and is adapted to be actuated longitudinally of the tube by the screw. It supports on its shoulder a washer it having a lug l9 that projects through the slot l l and is held against the shoulder by a coil spring 20. The spring is compressed by the axial movement of the screw and transmits the force to the movable plunger.

The distance which the spring is compressed serves as a measure of the magnitude of the pressure at the time the tablet is crushed. In order that the distance travelled by the lug may be estimated accurately a scale is provided consisting of a semi-circular plate 22, having a slotted portion, which is secured to the outer surface of the tube whereby the slot coincides with the slot of the tube and permits the lug to project therethrough. As a matter of convenience to the operator, the scale may be calibrated to read in pressure units, which in turn are a function of the extent of compression of the spring as evidenced by the travel of the lug. In order to avoid the necessity of a zero reading, the plate may be longitudinally, adjustably secured upon the tube, for example by means of screws 23 disposed in slotlike openings 24 in the plate whereby the lug will be at the zero reading when the plunger first engages the tablet. By means of this adjustment the device may be employed conveniently in testing tablets of different diameters.

In operating the device, the tablet is inserted against the base of the U-shaped member [2 and the screw is actuated until the plunger just engages the opposite peripheral surface of the tablet substantially as illustrated. This represents a zero reading for the lug on the scale. If desired and should it be necessary, the scale may be moved longitudinally in the proper direction until thereof directed longitudinally away from the the zero reading coincides with the zero mark on the scale. Thereafter the screw is turned in order to compress the spring gradually until the tablet fails. The reading is taken at the point of failure. Inasmuch as individual tablets vary somewhat even though they are prepared under practically identical conditions, several readings are desirable and an average thereof taken. For most pharmaceutical tablets the variation for individual tablets will not be more than 10%.

What we claim is:

1. An apparatus for testing the hardness of disc-like pharmaceutical tablets comprising a cylinder having a holder for tablets secured to one end thereof, a plunger slidably disposed in the cylinder and having a contact portion for engaging tablets upon the holder, a second plunger slidably disposed in the opposite end of the cylinder, a coiled compression spring disposed between the two plungers for resiliently urging them apart, but permitting relative movement therebetween, said cylinder having a longitudinal slot formed in the side wall thereof, a pointer secured to the second mentioned plunger and projecting through the slot, a scale for registering displacement of the pointer disposed adjacent to the slot, 2. cap having a threaded hole formed therein disposed upon the end of the cylinder opposite the tablet holder, and an actuating screw threaded into the hole and rotatably engaging the second mentioned plunger for purposes of actuating the latter toward the first mentioned plunger.

2. An apparatus as defined in claim 1 in which the tablet holder is in the form of a stirrup-like loop of trapezoidal configuration having the apex cylinder whereby to receive tablets disposed upon their edges.

3. An apparatus for testing the hardness of disc-like pharmaceutical tablets comprising a 5 cylinder having a tablet holder secured to one end thereof, the tablet holder being in the form of a loop of trapezoidal configuration and being open upon opposite sides to admit of disposing the tablets in peripheral contact with the loop during testing operations, the apex of the trapezoid being directed axially away from the cylinder, a plunger disposed within the cylinder and having a portion for engaging tablets disposed within the holder, resilient means for urging the plunger toward the tablets and additional means for registering the force exerted upon the plunger.

4. An apparatus for testing the hardness of disc-like pharmaceutical tablets, comprising a hollow member having a tablet holder secured to one end thereof, the tablet holder being in the form of a loop and being open upon opposite sides to admit of disposing the tablets in peripheral contact with the loop preparatory to testing, a plunger disposed within the hollow member and having a projecting portion for engaging tablets disposed within the holder, a helical spring engaging at one end with the plunger and actuating it toward the tablet holder, a second plunger engaging the opposite end of the spring, means for actuating the second plunger axially within the cylinder to compress the spring, and means connected to the second plunger for indicating displacement thereof.

FRANKLIN D. SMITH. LYNDALL GROSCH. 

